Field of the Invention
The present invention relates to special powdered coating materials. Furthermore, the present invention comprises the use of such powdered coating materials. Furthermore, the present invention comprises methods for substrate coating using such powdered coating materials.
Description of Related Art
A large number of coating methods for different substrates are already known. For example, metals or precursors thereof are deposited on a substrate surface from the gas phase, see e.g. PVD or CVD methods. Furthermore, corresponding substances can be deposited for example from a solution by means of galvanic methods. In addition, it is possible to apply coatings for example in the form of varnishes to the surface. However, all the methods have specific advantages and disadvantages. For example, in the case of deposition in the form of varnishes, large amounts of water and/or organic solvents are required, a drying time is needed, the coating material to be applied must be compatible with the base varnish, and a residue of the base varnish likewise remains on the substrate. For example, application by means of PVD methods requires large amounts of energy in order to bring non-volatile substances into the gas phase.
In view of the above-named limitations, a large number of coating methods have been developed to provide the properties desired for the respective intended use. Known methods use, for example, kinetic energy, thermal energy or mixtures thereof to produce the coatings, wherein the thermal energy can originate for example from a conventional combustion flame or a plasma flame. The latter are further divided into thermal and non-thermal plasmas, by which is meant that a gas is partially or completely separated into free charge carriers such as ions or electrons.
In the case of cold gas spraying, the coating is formed by applying a powder to a substrate surface, wherein the powder particles are greatly accelerated. For this, a heated process gas is accelerated to ultrasonic speed by expansion in a de Laval nozzle and then the powder is injected. As a result of the high kinetic energy, the particles form a dense layer when they strike the substrate surface.
For example, WO 2010/003396 A1 discloses the use of cold gas spraying as a coating method for applying wear-protection coatings. Furthermore, disclosures of the cold gas spraying method are found for example in EP 1 363 811 A1, EP 0 911 425 B1 and U.S. Pat. No. 7,740,905 B2.
Flame spraying belongs to the group of thermal coating methods. Here, a powdered coating material is introduced into the flame of a fuel gas/oxygen mixture. Here, temperatures of up to approximately 3200° C. can be reached for example with oxyacetylene flames. Details of the method can be learned from publications such as e.g. EP 830 464 B1 and U.S. Pat. No. 5,207,382 A.
In the case of thermal plasma spraying, a powdered coating material is injected into a thermal plasma. In the typically used thermal plasma, temperatures of up to approx. 20,000 K are reached, whereby the injected powder is melted and deposited on a substrate as coating.
The method of thermal plasma spraying and specific embodiments, as well as method parameters are known to a person skilled in the art. By way of example, reference is made to WO 2004/016821, which describes the use of thermal plasma spraying to apply an amorphous coating. Furthermore, EP 0 344 781 for example discloses the use of flame spraying and thermal plasma spraying as coating methods using a tungsten carbide powder mixture. Specific devices for use in plasma spraying methods are described multiple times in the literature, such as for example in EP 0 342 428 A2, U.S. Pat. No. 7,678,428 B2, U.S. Pat. No. 7,928,338 B2 and EP 1 287 898 A2.
In the case of high-speed flame spraying, a fuel is combusted under high pressure, wherein fuel gases, liquid fuels and mixtures thereof can all be used as fuel. A powdered coating material is injected into the highly accelerated flame. This method is known for being characterized by relatively dense spray coatings. High-speed flame spraying is also well known to a person skilled in the art and has already been described in numerous publications. For example, EP 0 825 272 A2 discloses a substrate coating with a copper alloy using high-speed flame spraying. Furthermore, WO 2010/037548 A1 and EP 0 492 384 A1 for example disclose the method of high-speed flame spraying and devices to be used therein.
Non-thermal plasma spraying is carried out largely analogously to thermal plasma spraying and flame spraying. A powdered coating material is injected into a non-thermal plasma and deposited with it onto a substrate surface. As can be learned for example from EP 1 675 971 B1, this method is characterized by a particularly low thermal load of the coated substrate. This method, particular embodiments and corresponding method parameters are also known to a person skilled in the art from different publications. For example, EP 2 104 750 A2 describes the use of this method and a device for carrying it out. For example, DE 103 20 379 A1 describes the production of an electrically heatable element using this method. Further disclosures in respect of the method or devices for non-thermal plasma spraying are found for example in EP 1 675 971 B1, DE 10 2006 061 435 A1, WO 03/064061 A1, WO 2005/031026 A1, DE 198 07 086 A1, DE 101 16 502 A1, WO 01/32949 A1, EP 0 254 424 B1, EP 1 024 222 A2, DE 195 32 412 A1, DE 199 55 880 A1 and DE 198 56 307 C1.
However, a general problem of coating methods using a powdered coating material is that under relatively gentle coating conditions only an insufficient coating quality is achieved. In particular, when there is an incomplete melting of the particles of the powdered coating material, cavities form which can for example influence the optical, haptic or electrical properties, the barrier effect and/or the heat conductivity of the coating.